1. Field of the Invention
The field of the invention is the providing of power for portable electronic devices, such as insulin pumps, analyte sensor devices, portable phones, personal digital assistants, etc. Specifically, the invention is directed to powering a portable electronic device for a known period of time after depletion of the main battery regardless of the type of battery that is installed in the portable electronic device.
2. Description of Related Art
Most portable electronic devices are powered by either an alkaline battery, a lithium-ion battery, or a rechargeable battery. FIG. 1(a) illustrates a voltage level over time provided by different types of batteries. As illustrated by Line A in FIG. 1(a), the alkaline battery starts out at a high voltage, e.g., approximately 1.55 volts, and decreases over time. Line D represents a battery threshold voltage. This low battery threshold voltage represents a value at which the battery is determined to be providing a low voltage. Once this threshold is reached, a message will need to be transmitted to a display of the portable electronic device indicating that the battery is running low, and should be replaced. If the portable electronic device is utilizing an alkaline battery, the voltage threshold may be around 1.16 or 1.08 volts. After the low battery threshold is reached in an alkaline battery, the alkaline battery can normally provide power to the portable electronic device for approximately twelve hours, assuming that the main battery life of the alkaline battery is 30 days. It should be noted that battery life is dependent on actual energy used by the device. Also, it also should be noted that due to the voltage threshold being around 1.1 volts, it is estimated that only two-thirds of the battery energy of the alkaline battery is utilized.
A lithium battery is capable of providing a much higher initial voltage and sustaining the value of that voltage for a long period of time. However, as illustrated by line B in FIG. 1(a), once the lithium battery becomes drained, the decrease in voltage value is rapid. If a lithium battery is being used in a portable electronic device, a user of the portable electronic device may have less than 30 minutes after receiving a low voltage message before the portable electronic device loses power. If the user is utilizing the portable electronic device for medical reasons, e.g., like an insulin pump, blood glucose sensor or meter, this may not provide the user with enough time to find a replacement battery.
A rechargeable battery can be a good economic solution for an owner of a portable electronic device. Rather than buying a new set of batteries every week or every month, the user may utilize household current to charge up the battery after the battery has expended its energy. Many portable electronic devices cannot utilize rechargeable batteries because the initial voltage supplied by the battery is too low and sometimes is not greater than the low battery threshold voltage set for alkaline batteries. The rechargeable battery has characteristics similar to the alkaline battery in terms of how long it can power a device, but as illustrated by Line C in FIG. 1(a), the initial voltage supplied by the rechargeable battery is lower than the initial voltage supplied by the alkaline battery. Accordingly, some initial voltages for rechargeable batteries may be lower than the low battery threshold voltage for the portable electronic device, as is mentioned above, and the portable electronic device may generate a message indicating that the rechargeable battery cannot be utilized. This is also true in regards to partially drained batteries, which may have low initial voltage readings.
In addition, the effective voltage of any of these batteries can be affected by the environment in which the battery is stored or utilized. For example, a temperature change in the environment in which the battery is located, can reduce the effective voltage provided by the battery. Also, subjecting the battery to vibration can result in a lowering of the effective voltage generated by the battery. This results in the battery providing a voltage reading that is lower than the low battery threshold and thus the portable electronic device may be unable to utilize the batteries subjected to changes in temperature as well as vibration.
Many current portable electronic devices that utilize a DC power source also include a backup battery system that provides a limited amount of functionality for the portable electronic device until the DC power source is replaced or recharged. In other words, the backup battery may provide enough energy to operate a run time clock for the portable electronic device and to save the contents of a memory, but does not provide power for full functionality of the portable electronic device.